South Korea is known as a nation capable of producing a mass amount of lithium secondary batteries, and occupies 40% of the worldwide production capacity of the cathode active materials for secondary batteries. Therefore, South Korea imports about 15,000 tons of lithium carbonate to produce the cathode active materials. A process of recycling discarded lithium secondary batteries is classified into a dry process and a wet process. In the dry process, discarded lithium secondary batteries are introduced into a high-temperature furnace to recover metals, which is relatively simple. However, the dry process is expensive in terms of initial investment cost. In addition, a metal recovery rate is poor, and gas treatment cost is high disadvantageously. In comparison, in the wet process, discarded lithium secondary batteries are dissolved in sulfuric acid, and metals are extracted using a solvent extraction method. The wet process is advantageous in terms of an inexpensive initial cost, a high metal recovery rate, and a high purity. However, a cost for treating a waste liquid of the solvent extraction is expensive disadvantageously.
In South Korea, the amount of discarded lithium secondary batteries is estimated to about 20,000 tons per year. Out of this amount, it is known that about 3,000 tons of metal scraps are generated in the process of recovering metals from the discarded lithium secondary batteries. The process of recovering metals from discarded lithium secondary batteries is mainly a solvent extraction process for recovering cobalt and nickel from discarded cathode active materials. Through the solvent extraction process, a manganese sulfate waste liquid and a lithium sulfate waste liquid are generated abundantly. Since the manganese sulfate waste liquid and the lithium sulfate waste liquid are heavy metals, an unfiltered discharge to the nature is inhibited. In this regard, a purification process or a strategy for extracting useful metals from the waste liquid has been studied in the art.
An annual metal recovery capacity of the main domestic discarded lithium secondary battery recycling companies is estimated to 12,000 tons per year. Assuming that the factories are fully operated, 12,000 tons of the manganese sulfate waste liquids and 180,000 tons of lithium sulfate waste liquids are generated. It is predicted that the metal recovery facilities will be established more and more, and the waste liquid amount also increases in the future as the domestic use amount of the discarded lithium secondary batteries increases in South Korea.
The amount of the lithium sulfate waste liquid is abundant, and a lithium concentration of the lithium sulfate waste liquid is very high (approximately 3,000 ppm). Therefore, development of a lithium recovery technology is highly demanded. However, existing methods using a series of processes including (absorption)-(descorptive condensation)-(solvent extraction or evaporative condensation)-(solvent extraction) are expensive (about $5/ton in the case of lithium carbonate). This makes it difficult to apply the existing methods. Therefore, there is an urgent demand for a technology that enables production of lithium carbonate with an inexpensive treatment cost relative to the existing processes.
The patent documents and references cited herein are hereby incorporated by reference to the same extent as if each reference is individually and clearly identified.